Pinocytosis is a type of endocytosis where a cell engulfs any extracellular fluid that is present, including water and dissolved nutrients. Curved pits are rapidly formed when structural proteins, such as clathrin triskelions, assemble and coat the cytosolic side of the plasma membrane. This process is non-specific because there are no receptors to bind particular substances on the outside. Rather, the pocketed contents are pinched off into a coated vesicle and then are ready to be transported throughout the cell.